Load compensated control system



July 23, 1940. Hb E, HAR-HG Er AL 2,208,752

LOAD coMPENsATED CONTROL SYSTEM Filed NOV. 23, 1956 gwn :MM

Henwg/Ejfaftzg CWZQS B. parztgefzbeflg Patented lJuly 23, 1940 UNITED STATES PATENT 'i OFFICE LOAD COMTENSATED CONTROL SYSTEM Henry E. mung, -Robbinsdala and chariesf. Spangenberg, Minneapolis,.Minn., assignors ,to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application November'23, 1936, Serial No. 112,340

12 claims. (ci. :23e-17s) l'I'his invention relates )to automatic reset or load' compensation mechanism as applied to a follow-up control system.

Itis` an object of this invention to provide ay follow-up control system which controls the value of a condition along witha novel automatic reset or load compensation mechanism formamtaining the value of the condition to be controlled substantially constant l regardless of changes in load.

Another .object is to provide a simple means for varying the rate of reset so that the system may beadapted for universal application.

The construction andmode of operation of the combined follow-up control system and automatic reset mechanism also formA objects of this invention.

Other objects and advantages will become apparentto those skilled in the art upon reference o. to the accompanying specification, claims and drawing.

Fora more thorough understanding of this inventionref'erence is made to-theaccompanying vsingle sheet of drawing, in which is diagrammati- 25` cally disclosed the preferred form oi this invention. -1

Referring now to the'drawing, a device to be positioned in `a plurality of positions for controlling the value of a condition is generally designated at I0. Control means the state of which is varied in accordance with changes in the value of the condition to be controlled 1s generally designated at II. The control means II is adapted to control the operation of a relay generally des- 35 ignated at I2. The relay I2 positions a motor generally'designated at I3 which in turn positions thedevice III and also operates a follow-up means generally designated at I4. The follow-up means I4 also controls the operation of therelay 40 I2 to provide a true follow-up system. An automatic reset mechanismgenerally designated at I5 further controls the operationof the relay I2 to maintain the value of the condition to be controlled at the desirednormal value. regardless of 45 changes in load.

Although the control system of this vinvention may be utilized vfor controlling any desired condition it is 'disclosed for purposes of illustration as controlling a temperature condition and more .50 particularly the temperature of av space, not

shown. Therefore, the device I0 which is positioned in a plurality of positions is shown to comprisel a valve I6. forA controlling the supply of heating fluid to the space. 'I'he valve I6 may be 55 operated by a valve stem I1 which is connected by a pitman I6 to a crank disc I9 carried b y a shaft of the motor I3. v'I'he shaft`26 is operated throughy areduction gear train 2| by motor --rotors 22 and 23. v'I'he rotors 22 and 23 are oper- 60 ated by field vwindings 24 and 25, the arrangement being .such that when the eld winding v24 is energized the valve I6 is moved towards an open position and when the field Winding 25 is energized'thel valve I6 is moved toward a closed position. i i v l 'I'he shaft 20 also operates an abutment memi ber 26 for opening limit switches 21 and 28 when the valve I6 is moved toan extreme closed position and an vextreme open position respectively. 'I'he shaft26 also operates a slider 30 with respect 1 to a resistance element 3I. The slicler 3U and the resistance element '3| form a balancing impedance means or potentiometer and therefore comprise the follow-up means I4. When the valve I6 is moved towards an open position the slider 15.

3II is moved towards the left and when the valve i I6 is moved towards a'closed position the slider 30 is moved towards the right.

The control means generally designated at II Iis shown to be a thermostatic 'control means hav- 20 ing a thermostatic element 33 responsive to variations in space temperature. Thermostatic element 33 may be of the usual bellows type containing avolatile uid. Thermostaticdevice 33 operates a bell'crank lever 34 which is connected 25 by a crank 35 to a lever 36 pivoted at 3l. Lever 36 carries a slider38v which Vis adapted to slide across'a resistance element 39. 'I'he slider 36 and the resistance element 39 form a control impedance means in the form of a potentiometer. The 30 lever 36 also operates a resilient switch arm 4|! with respect tov contacts 4I and 42. The temperature setting ofthe thermostatic control means may be adjusted by suitably adjusting the tension in a spring 43 connected to the Ybell crank 35 lever 34. Upon an increase in space temperature the bellows 33 expands and moves the slider 38 to the left in the direction indicated by the character H and moves the'switch arm 40 into engagement with the contact 42. Upon a decrease 't The relay generally designated at I2 may comprise electrical operating means such as relay coils 45 and 46 for moving an armature 41. 4The 65 relay I2 lalso includes-other electrical operating means vsuch as relay coils 48 and 49 for further operating the armature 4'I. The armature 4'I is suitablyconnected to a switch arm 50 which is adapted" to .engage spaced contacts 5I and 52. 60

Omltting the eiect of the relay coils 48 and 49, the switch arm 58 is moved into engagement with the contact 5I when the relay coil 45 is energized more than the relay coil 46 and the switch arm 58 is moved into engagement with the contact 52 when the relay coil 46 is energized more than the relay coil 45. In a like manner, omitting the controlling eiect of the relay coils and 46 the switch arm 58 is moved into engagement with the contact 5| when the relay coil 48 is energized more than the relay coil 49 and is moved into env gagement with the contact 52 when the relay coil 49 is energized more than the relay coil 48. Therefore, it is seen that when the total energizations of the relay coils 45 and 48 are greater than the total energizations of the relay coils 46 and 49, the switch arm 58 is moved into engagement with the contact 5|. When the total energizationsvof the relay coils 46 and 49 are greater than the total energizations of the relay coils 45 and 48, the switch arm 58 is moved into engagement with the contact 52. When-the energizations of the relay coils 45 and 48 are equal to the energizations of the relay coils 46 and 49 the switch arm 58 is maintained spaced midway between the contacts 5I and 52' as shown in the drawing.

Power is supplied to the relay I2 by means of a step down transformer 53 having a primary 54 connected across line wires 55 and 56 and a secondary 51. One end of the secondary 51 is connected by a wire 58 to the left ends of the relay coils 45 and 48. The other end of the secondary 51 is connected by a wire 59 to the right ends of the relay coils 46 and 49. The adjacent ends of the relay coils 45 and 46 andthe relay coils 48 and 49 are connected together. By reason of -these connections it is seen that the relay coils 45 and 46 are connected in series across the secondary 51 of the transformer and also that the relay coils 48 and 49 are connected in series and across the secondary 51. The left end of the relay coil 45 is connected by a protective resistance 6| and wires 62 and 63 to the left ends of the control potentiometer resistance elementV 39 and the balancing potentiometer resistance element 3|. In a like manner the right end of the relay coil 46 is connected by a protective resistance 64 and wires 65 and 66 to the right ends of the control potentiometer resistance element 39 and the balancing potentiometer resistance element 3|. The junction of the relay coils 45 and 46 is connected by wires 61, 68 and 69 to the slider 38 of the control potentiometer and the slider 30 of the balancing potentiometer. By reason of these wiring connections it is seen that the control potentiometer and the balancing potentiometer are connected in parallel with the series connected relay coils 45 and 46 and across the secondary 51.

Omitting for the time being the action of the relay coils 48 and 49 it is assumed that the parts are in the position shown in the drawing. The space temperature is at the desired normal value and the valve I6 is in a midposition for supplying just the correct amount of heat to make up for the heat losses `from the space. Upon an increase in the heating load the space temperature decreases and the slider 38 is moved to the right in the direction indicated by the character C. By reason of the above referred to parallel relationship this right-hand movement of the slider 38 decreases the energizations of the relay coil 46 and increases the energization of the relay coil 45 to move the switch arm 58 into engagement with the contact 5I to complete a circuit from the line wire 55 through wire |08, switch arm 50, contact 5|, wire |82, limit switch 28, wire |83, eld winding 24 and wire |85nback to'the other line wire 56. Completion of this 5 circuit energizes the eld windingV 24 to move the valve I6 towards an open position which increases the supply of heat to the space. Operation of the motor I3 to move the valve I6 towards an open position also moves the slider 38 of the l0 balancing potentiometer to the left. Movement of the slider 38 to the left decreases the energization of the relay coil 45 and increases the energization of the relay coil 46. When the slider 38 has moved sufciently far to the left to rel5 balance the energizations of the relay coils 45 and 46 the switch arm 58 is moved out of engagement with the contact 5| to break the circuit through the eld winding 24. In this manner the valve I6 is modulated towards an open position in direct accordance with the amount of decrease in space temperature. Upon a decrease in the heating load which causes an increase in space temperature the slider 38 of the control potentiometer is moved '25 to the left in the direction indicated by the character H. This left-hand movement of the slider 38 decreases the energization of the relay coil 45 and increases the energization of the relay coil 46 whereupon the switch arm 58 is moved into engagement with the contact 52 to complete a circuit from the line wire 55 through wire |08, switch arm 58, contact 52, wire |86, limit switch 21, wire |01, eld'winding 25 and wire |85 back to the other line wire 56. Completion of this '35 circuit energizes the field winding 25 to move the valve I6 towards a closed position to decrease the supply of heat to the space. Operation of the motor I3 to move the valve I6 towards a closed position also causes right-hand movement of the slider 38 of the balancing potentiometer. 'I'his right-hand movement of the slider 38 decreases the energization of the relay coil 46 and increases the energization of the relay coil 45. When the slider 38 has moved suiciently far to the right to rebalancethe energization of the relay coils 45 and-46 the switch arm 58 is moved out of engagement with the contact 52 to break the circuit through the iield winding 25. In this manner the valve I6 is modulated towards 50 a closed position in direct accordance with the amount of increase in space temperature.

By reason of the above construction and mode of operation a true follow-up control system is aorded. It is found that if the control range 55 of the control potentiometer is made suiiciently narrow to give accurate' temperature control hunting is likely to occur. Also it isJfound that if the control range is made suiciently wide to prevent hunting a noticeable droop in the 60 space temperature becomes apparent, that is, the space temperature is maintained at a lower value when the heating load is relatively great than when the heating load is relatively light. In order to eliminate hunting the control range of 05 the control potentiometer is widened and in order to eliminate the drooping characteristic of the/.- follow-up control system the automatic reset mechanism generally designated at I5 is utilized.

The automatic reset mechanism I5 may com- 70 prise a compensating impedance means in the form of a potentiometer formed by a slider 1| adapted to slide across a resistance element 12. Slider 1I is operated by a shaft 13 which is driven through a reduction gear train 14 by motor 'f rotors and 18. The rotors 15 and16 are controlled by field windings 11 and 18. The `arrangement is such that when the field winding 18 is energized the slider 1| is moved to the right and when the eld winding 11 is energized the slider 1| is moved to the left. Shaft 13 also operates an abutment member y 19 for opening limit switches 88 and 8| when the slider 1| isv moved to an extreme right-hand position or an extreme left-hand position respectively. 'I'he left end of the compensating potentiometer resistance element 12 is connected` by a wire 82 and a protective resistance to the left end of the relay coil 48. 'Ihe right end of the compensating potentiometer resistance element 12 is connected by a wire 84 and aprotective resistance 85 to the right end of the relay coil 49. Slider 1| of the compensating potentiometer is connected by ywire 88 to a contact 81 which is adapted to be manually positioned with respect to a resistance element p 88. 'Ihe contact 81 and the resistance element 88 form an adjustable impedance means or rheostat. Resistance element 88 is connected by a wire 89 to the junction of the relay coils 48 and 49. By reason of these wiring connections it is seen that the compensating potentiometer is connected in parallel withthe series connected relay coils 48 and 49 and across the secondary 51.

In order to explain the operation of the follow-up system yin combination with the reset mechanism it is assumed that the parts are in the position shown in the drawing. Upon an increase in the heating load the space temperature decreases and the slider 38 is moved to theright in the direction indicated by the character C. This increases the energization of the relay coil 45 and decreases the lenergization o f the relay coil 48 to move the valve I6 towards anv open position and to move the slider 38 to the left to rebalance the energization of the relay coils 45 and 46. In this manner the valve'l6 is modulated towards an open position in accordance with the amount of decrease in space temperature as pointed out above. A decrease in space temperature also moves the switch arm 48 into engagement with the contact 4| to complete a circuit from a line wire 9| through wire 92, switch arm 40, contact 4|, wire 93, limit switch 88, wire 94, eld winding 18 and' wire 95 back to the other line wire 96. Completion of this circuit energizes the eld winding 18 to move the slider 1| towards the right. Movement of the slider '1| towards theright decreases the energization nf the relay coil 49 yand increases the energization of the relay coil 48, whereupon the switch arm 58 is moved into engagement with the contact 5|. This causes further opening movement of the valve I6 and left-hand movement of the slider 30. This left-hand movement of the slider 38 unbalances the energization of the relay coils ,45 and 46 to decrease the energization of coil *'45 and increase the energization of coil 46. When the total energizationsof the relay coils 45 and 48 equals the total energization of the.relay coils 46 and 49, the switch arm 58 moves out of engagement with the contact 5| and the valve I6 is maintained in the new position. Therefore, as long as the slider 1| is moving towards the right the valve I6 is being positioned further towards an open position and the slider 1| will continue in its movement towards the right asA long as the space Atemperature is less than the `desired normal value. As a result of this additional opening movement of the valve I6 additional heat is supplied to the space to restore the space temperature to the desired .normal value. When this happens the switch arm 48 moves out of engagement with the contact 4| to break the circuit through the .field winding 18 and prevent further right-hand movement of the slider 1|. The valve I6 is therefore re-positioned or reset towards the open position by the automatic reset mechanism l5 in direct accordance with the amount of the increase in heating load.

Upon a decrease in the heating load the space temperature increases and the slider 38 of the control potentiometer is moved to the left in the direction indicated by the character H. The motor i3 is thereupon operated to move the valve i8 toward a closed position and to move the slider 38. of the balancing potentiometer to the right to"rebalance the energization of the relay l coils 45 and 45. The valve i8 is therefrom modulated towards a closed position in accordance with the amount of increase in space temperature in the manner pointed out above. An ihcrease in space temperature caused by the decrease in heating load also moves the switch arm 48 into engagement with the contact 42 to complete a circuit from the line wire 9| through wire 92, switch arm 48, contact 42, wire 91, limit switch 8|, wire 98, iield winding 11 and wire 95r back to the other line wire 98. Completion of this circuit energizes the field winding 11 to move the slider 1| of the compensating potentiometer towards the left. Movement of the slider 1| of the compensating potentiometer towards the left decreases the energization of the relay coil 48 and increases the energization of the relay coil 49 to move the switch arm 58 into engagement with the contact 52 whereupon the field winding is energized and the valve I6 is moved further towards a closed position. Movement of the valve I6 towards a closed position causes right-hand movement of the slider 38 kof the balancingpotentiometer which decreases the energizationof the relay coil 46 and increases the energization of the relay coil 45. When the slider 38 has moved sufficiently far towards the right so that the total energizations of the relay coils and 48 equal the total energizations of the relay coils 48 and 49, the switch arm 58 is moved out of engagement with the contact 52 and further opening movement of the valve |6 is stopped. As long as the space temperature is above the desired normal value the slider 1| of the compensating potentiometer will continue in its left-hand movementand the valve I6 will be continued in its movement towards the closed position. By reason of this additional decrease in the supply of heat to the space the increase inv load is compensated for and the slider' 38 of the control potentiometer is moved back to the mid position as shown in the drawing and also the switch arm 48 is moved out of engagement .with the contact 42. When the switch arm 48 moves out of engagement with the contact 42 the field winding 11 is deenergized and further lefthand movement of the slider 1| of compensating potentiometer `is stopped. Therefore, the valve I6 is repositioned or reset further towards a closed position with respect to the value of the space temperature in direct accordance with the amount of decrease in the heating load.

By reason of the above construction and mode of operation av control system is provided wherein the spacetemperature is maintained at a substantially constant value without hunting and regardless oiv changes in the heating load. In

order to properly adjust the control system so that its application may be universal, some means must be provided for adjusting the rate of reset. That is, some means must be provided for adjusting the rate at which the valve I6 is further positioned towards its open or closed positions. This rate adjustment is accomplished by means of the rheostat connected in series with the slider" 'H of the compensating potentiometer. By adjusting the rheostat the relative unbalance of the energizations of the relay coils 48 and 49 are adjusted. By moving the contact 81 to the right to increase the resistance in series with the slider 1l of the compensating potentiometer the unbalance of the energization of the relay coil 48 .is decreased and therefore a less amount of movement of the slider 30 of the balancing potentiometer is required to rebalance the relay I2. It follows, then, that if less amount of movement of the slider 30 is necessary the valve I8 will not be repositionedl as rapidly or as far and therefore the rate of reset of the valve I6 is decreased. By moving the contact 81 of the rheostat to the left to decrease the resistance in series with the slider 'Il of the compensating potentiometer the relative unbalance of the energizations of the relay coils 48 and 49 is increased and a greater movement of the slider 30 of the balancing potentiometer is required to rebalance the relay I2. It follows then that if -a greater amount of movement of the slider 30 is required to rebalance the relay I2 the valve IE- will be repositioned or reset further towards the openl or closed position a greater amount and at a faster rate. This simple manner of adjusting the rate of reset is made possible by reason of the compensating potentiometer being connected magnetically as distinguished from electrically to the remainder of the follow-up control system.

From the above it is seen that we have provided a follow-up control system along with a novel automatic reset or load compensation mechanism whereby the value of a condition may be maintained at a substantially constant value regardless of changes in load and wherein simple means are provided for adjusting the rate of reset.

Although for purposes of illustration we have disclosed one form of this invention, other forms thereof may become obvious to those skilled in the art upon reference to this specification and therefore this invention is to be limited only by the scope of the appendedclaims and the prior art.

We claim as our invention:

1. In combination, a device to be positioned in a plurality of positions for controlling the`value of a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, means including electrical operating means and a control member positioned thereby for positioning said device, electrical connections between the control impedance means and the electrical operating means to position said device in accordance with changes in the-value of the condition to be controlled, adjustable compensating impedance means adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other electrical operating means for positioning said control member, and electrical connections between the compensating impedance means and. the other electrical operating means for positioning said device differently with respect to the value of the condition tol loe controlled.

2. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, means including electrical operating means and a control member positioned thereby for positioning said device, electrical connections between the control impedance means and the electrical operating means to position said device in accordance with changes in the value of the condition to be controlled, adjustable compensating impedance means, reversible m'otor means operated as an incident to deviation of the value of the condition to be controlled from the desired normal value for adjusting the compensating impedance means, other electrical operating means for positioning said control member, andelectrical connections between the compensating impedance means and the other electrical operating means.

3. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, means including electrical operating means and a control member positioned thereby for positioning said device, electrical connections between the control imlpedance means and the electrical operating means to position said device in accordance with changes ln the value of the condition to be controlled, adjustable compensating impedance means, reversible motor means operated in response to deviation of the value of the condition to be controlled from the desired normal value for adjusting the compensating impedance means, other electrical operating means for positioning said control member, and electrical connections between the compensating impedance means and the other electrical operating means.

4. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustable control impedance means adjusted in accordance with-changes in the value of the condition to be controlled, means including electrical operating means and a control member positioned thereby for positioning saidl device, electrical connections-between the control impedance means and the electrical operating means to position said device in accordance with changes in the value of the condition to be controlled, adjustable compensating impedance means adjusted as an incident to deviation of the value of the condition to becontrolled from the desired normal value, other electical operating means forpositioning said control member, electrical connections between the compensating impedance means and the other electrical operating means for positioning said device differently with respect to the value of the condition to be controlled, and means for adjusting the operating effect of the other electrical operating means on the control` member.

5. In combination, a device to be positioned in a plurality of positions for controlling the value of f a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, means including electrical operating means anda control memberl positioned thereby for positioning said device, electrical connections between the control impedance means and the electrical operating means to position said device in accordance with changes in the value of the condition to be controlled, adjustable compensating impedance means, reversible motor means operated as an incident to deviation of the value of the condition to be controlled if from the desired normal value for adjusting the compensating impedance means, other electrical operating means for positioning said control member, and electrical connections between the compensating impedance means and the other electrical operating means, and means for adjusting the operating eiect of the other electrical operating means on the control member.

6. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an armature controlled thereby for positioning said device, connections between the control impedance means andthe inductance means for positioning said device in response to changes in the value of the condition to be controlled, adjustabler compensating impedance means adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other inductance means for controlling the armature, and connections between the compensating impedance means and the other inductance means.

7. In combination, a device to be positioned in a plurality of positions for controlling the value oi a condition, an adjustable control potentiometer adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an armature controlled thereby for positioning said device, connections between the control potentiometer and the inductance means for positioning said device in response to changes in the value of the condition to be controlled, an adjustable compen` sating potentiometer adjusted as an incident to deviation of the value of the condition to be convtx'olled from the desired normal value, other inductance means `for controlling the armature, and connections between the compensating potenti- Y ometer and the other inductance means.

. 8. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustable control impedance means adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an arma. ture controlled thereby for positioning said device, connections between the control impedance means and the inductance means for positioning said device in response to changes in the value of the condition to be controlled, adjustable compensating impedance means'adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other inductance means for controlling the armature,

connections between the compensating impedance means and the other inductance means, and means for adjusting the controlling eiect of the other inductance means on the armature.

9. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, an adjustable control potentiometer adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an armature controlled thereby for positioning said device, connections between the control potentiometer and the inductance means for positioning said device in response to changes in the value of the condition to be controlled, an adjustable compensating potentiometer adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other introl member positioned thereby for positioningsaid device, electrical connections between the control impedance means and the electrical operating means to position said device in accordance j with changes in the value of the condition to be controlled, adjustable compensating impedance means adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other electrical operating means for positioning said control member, electrical connections between the compensating impedance means and the other electrical operating means for positioning said device differently with respect to the value of the condition to be controlled, and means for adjusting the operating eiTect of the other electrical operating means on the control member, said last mentioned means including adjustable impedance means in the last mentioned electrical connections.

11. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, adjustablel control impedance means adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an armature controlled thereby for positioning said device, connections between the control impedance means and the inductance means for positioning said device in response to changes in the value of the condition to be controlled, adjustable compensating impedance means adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other 'inductance means for controlling the armature,

connections between the compensating impedance means and the other inductance means, and means for adjusting the controlling eiect of the other inductance means on the` armature, said last mentioned means including adjustable impedance means in the last mentioned connections.

12. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, an adjustable control potentiometer adjusted in accordance with changes in the value of the condition to be controlled, relay means including inductance means and an armature controlled thereby for positioning said device. connections between the control potentiometer and the inductance means for positioning said device in response to changes in the value of the condition to be controlled, an adjustable compensating potentiometer adjusted as an incident to deviation of the value of the condition to be controlled from the desired normal value, other inductance means for controlling the armature, connections between the compensating potentiometer and the other inductance means, and

means for adjusting the controlling e'ect of the other inductance means on the armature, said last mentioned means including adjustable resistance means in the last mentioned connections.

HENRY E. HARTIG. CHARLES B. SPANGENBERG. 

